Ability of Ru complexes for ROMP tuned through a combination of phosphines and amines

Polynorbonerne with high molecular weight was obtained via ring opening metathesis polymerization using catalysts derived from [RuCl2(PPh2Bz)2L] (1 for L = PPh2Bz; 2 for L = piperidine) type of complexes when in the presence of ethyl diazoacetate in CHCl3. The polymer precipitated within a few minutes at 50 °C when using 1 with ca. 50% yield ([NBE]/[Ru] = 5000). Regarding 2, for either 30 min at 25 °C or 5 min at 50 °C, more than 90% of yields are obtained; and at 50 °C for 30 min a quantitative yield is obtained. The yield and PDI values are sensitive to the [NBE]/[Ru] ratio. The reaction of 1 with either isonicotinamide or nicotinamide produces six-coordinated complexes of [RuCl2(PPh2Bz)2(L)2] type, which are almost inactive and produce only small amounts of polymers at 50 °C for 30 min. Thus, we concluded that the novel complexes show very distinct reactivities for ROMP of NBE. This has been rationalized on account of a combination of synergistic effects of the phosphine–amine ancillary ligands.

Graphical abstractDifferent Ru(II) complexes show distinct reactivities for ROMP of norbornene on account of a combination of synergistic effects of the ancillary ligands. The propagating species are hybrid amine–phosphine complexes. For example, [RuCl2(PPh2Bz)3] was not active at room temperature, whereas [RuCl2(PPh2Bz)2(piperidine)] showed 92% yield for 30 min at 25 °C with [NBE]/[Ru] = 5000.Figure optionsDownload full-size imageDownload as PowerPoint slide